This invention relates to an apparatus for generating a high-pressure gas, and more particularly to an apparatus by which a fuel mainly comprising lithium, magnesium, aluminum, boron or like light metal or a compound thereof is reacted in molten state with water by contact therewith to produce a high-temperature high-pressure combustion gas for use as driving energy for turbines or the like to propel self-propelling submarine bodies.
High pressure gas generating apparatus must have a high gas generating efficiency and must be so designed that the peripheral wall of the combustion chamber is prevented from overheating.